Cylinder for power steering system with releasable hydraulic stops

ABSTRACT

A fluid operated power steering system having a control motor for actuating a steering valve which, in turn, actuates a fluid operated steering motor, the system including manually operable control means for delivering fluid under pressure from a pump to opposite ends of the control motor selectively. The control motor includes a control cylinder having axial cylindrical recesses at its ends, and includes a control piston having on opposite sides thereof complementary axial cylindrical plungers respectively insertable into the recesses so that fluid trapped in the recesses provides hydraulic stops for the control piston at the ends of its stroke. A relief valve discharges fluid from the recesses into a reservoir in the event excessive pressures are developed in the recesses due to external forces, such as the encountering of obstructions by the steerable wheels of the vehicle on which the system is installed. Under such conditions, the control system overrides the hydraulic stops and encounters mechanical stops at the ends of the control cylinder. With this construction, the hydraulic stops normally limit the travel of the control piston, but can be overcome if necessary to permit overtravel of the steerable wheels. Under such conditions, the hydraulic stops have a cushioning effect on the control piston and limit the severity of contact with the mechanical stops.

United States Patent Garrison et al.

[54] CYLINDER FOR POWER STEERING SYSTEM WITH RELEASABLE I HYDRAULICSTOPS [72] Inventors: Robert A. Garrison, Newport Beach; Leonard L.Conopa, Westminster, both of Calif. [73] Assignee: GarrisonManufacturing Co., Inc.,

' Santa Ana, Calif.

[22] Filed: Nov. 27, 1970 [21] Appl. No.: 93,044

[52] US. Cl ..l80/79.2 R, 60/52 S, 91/405, 92/85 [51] Int. Cl. ..B62d5/06 [58] Field of Search ..l.80/79.2 R; 60/52 S; 91/26, 91/396, 404,405, 406, 407; 92/85 [56] References Cited I UNITED STATES PATENTS3,602,326 8/1971 Garrison ..180/79.2 R 3,175,725 3/1965 Sampson ..91/26X 2,824,447 2/1958 Garrison ..l80/79.2 R 3,291,245 12/1966 Hewko..l80/79.2 R R23,867 9/1954 Garrison ..180/79.2 R 2,911,952 11/1959Peras ..91/405 X 3,196,753 7/1965 Maurer ..91/26 3,247,767 4/1966 Asian..91/396 X 3,260,167 7/1966 Pedersen et al ..91/396 X FOREIGN PATENTS ORAPPLICATIONS 527,013 10/1940 Great Britain ..l80/79.2 R

[451 Oct. 3, 1972 [57] ABSTRACT A fluid operated power steering systemhaving a control motor for actuating a steering valve which, in turn,actuates a fluid operated steering motor, the system including manuallyoperable control means for delivering fluid under pressure from a pumpto opposite ends of the control motor selectively. The c0ntrol motorincludes a control cylinder having axial cylindrical recesses at itsends, and includes a control piston having on opposite sides thereofcomplementary axial cylindrical plungers respectively insertable intothe recesses so that fluid trapped in the recesses provides hydraulicstops for the control piston at the ends of its stroke. A relief valvedischarges fluid from the recesses into a reservoir in the eventexcessive pressures are developed in the recesses due to externalforces, such as the encountering of obstructions by the severity ofcontact with the mechanical stops.

1 Claim, 3 Drawing Figures ..returning itto a reservoir connectedBACKGROUND OF INVENTION The present invention relates in general to apower steering system and, more particularly, to a fluid operated systemgenerally similar to those disclosed in Garrison U.S. Pat. No. Re.23,867, reissued Sept. 14, 1954, and in Garrison U.S. Pat. No.2,824,447, issued Feb. 25, 1958. Each of these patents discloses avehicle having some steerable means, such as steering arms or a steeringlinkage connected to steerable wheels, which is acted on by a fluidoperated steering motor of the reciprocating type controlled by asteering valve having a reciprocable valve element of the spooltype'therein. In each instance, a manual steering input displaces thevalve element of the steering valve in one direction or the other tocause the steering motor to displace the steerable meanscorrespondingly. The steering valve disclosed in each of these patentsincludes aball stud which engages the valve element anddetermines itsposition ,relative' to the ports inthe housing of the steering valve inresponse to a manual steering input force.

The fluid operated power steering system of each of the aforementionedpatents also includes a steering pump which supplies fluid underpressure to the steering valve, the latter, in turn, delivering thefluid under pressure to one end or the other of thesteering motor, or,in the absence of a steering input force, simply to the steering pumpinlet. r

The present invention involves a steering, motor, steering valve andsteering pump and reservoir as sembly identical in principle to thosedisclosed in Garrisons aforementioned patents. The latter are,therefore, incorporated herein by reference.

The present invention further involves a control motor which isconnected to the steering valve to form a steering valve link, and whichactuates the steering valve in response to selective application offluid pressure to opposite ends of the control motor. A manuallyoperable control means delivers fluid under pressure from the steeringpump to opposite ends of the control motor selectively.

SUMMARY AND OBJECTS OF INVENTION With the foregoing as background, aprimary object of the invention is to provide a fluid operated powersteering system of the nature outlined wherein the control motor isprovided with hydraulic stops limiting the travel of the control pistonthereof, and wherein the steering system is provided with means foroverriding the hydraulic stops in the event that external forces appliedto the steerable wheels, or other steerable means, require overtravel ofthe steerable means. For example, such external forces may result fromobstructions encountered by the steerable wheels.

With the foregoing construction, the hydraulic stops normally limit thetravel of the control piston, but can be overriden if necessary topermit overtravel of the steerable means. 1

A further object is to provide the control motor with mechanical stopsfor the control piston which are operative when the hydraulic stops areoverriden. Under such conditions, the hydraulic stops have a cushioningeffect which limits the engagement forces between the control piston andthe mechanical stops, which is another feature of the invention.

More particularly, an important object of the inven- I tion is toprovide the control cylinder with axial cylindrical recesses at its endsand to provide the control piston on opposite sides thereof withcomplementary axial cylindrical plungers respectively insertable intothe recesses so that the fluid trapped in the recesses stops the controlpiston at the ends of its stroke.

Still another important object is to provide relief valve meansconnected to the recesses for discharging trapped fluid therefrom intothe reservoir to permit overtravel of the control piston whenever thisis necessary to permit overtravel of the steerable means, in response toencountering an obstruction, for example.

The foregoing objects, advantages, features and results of the presentinvention, together with various other objects, advantages, features andresults thereof which. will be evident to those skilled in the fluidoperated power steering art in the light of this disclosure, may beachieved with the exemplary embodiment of the invention described indetail hereinafter and illustrated in the accompanying drawings.

DESCRIPTION OF DRAWINGS In the drawings: FIG. 1 is a diagrammatic viewof a fluid operated power steering system embodying the invention;

FIG. 2 is a longitudinal sectional view of a control motor incorporatedin the power steering system of FIG. 1 and embodying the invention, thecontrol piston of the control motor being shownin an intermediateposition; and v FIG. 3 is an enlarged view similar to FIG. 2, but

I i showing the control piston at one end of its stroke.

DESCRIPTION OF EXEMPLARY EMBODIMENT OF INVENTION fluid operated powersteering system for a vehicle having a frame shown fragmentarily at 12and having steerable means 14. The latter is shown for purposes ofillustration as including a steering arm 16 connected to a steerablewheel 18. Of course, the vehicle may include two steerable wheels havingsteering arms interconnected by a tie rod, not shown.

The power steering system 10 includes a fluid operated steering motor 20of the reciprocating type connected at one end to the frame 12 and atits other end to the steering arm 16. The steering motor 20 is connectedto and controlled by a steering valve 22 of the typedisclosed in theaforementioned patents. The steering valve 22 constitutes one end of asteering valve link 24 which is connected at one end to the frame 12 andat its other end to the steering arm 16, the other end of the steeringvalve link 24 comprising a fluid operated control motor 26 of thereciprocating type. As shown in FIGS. 2 and 3, the control motor 26includes a control cylinder 28, one end of which is connected to thehousing of the steering valve 22. Rcciprocable in the control cylinder28 is a control piston 30 connected to a piston rod 32 which projectsfrom the other end of the control cylinder and is connected to thesteering arm 16.

Reverting to FIG. 1 of the drawings, the steering valve 22 controls thesteering motor 20 through interconnecting fluid lines 34 and 36. Thesteering valve 22 is supplied with operating fluid under pressure by asteering pump 38 through a fluid supply line 40. A fluid return line 42connects the steering valve 22 to a reservoir 44, the latter beingconnected to the inlet of the steering pump 38 through a fluid inletline 46.

The fluid operated power steering system of the v invention includesmanually operable control means 50 for delivering fluid under pressurefrom the steering pump 38 to the control cylinder 28 on opposite sidesof the control system 30 selectively, depending on the direction inwhich it is desired to steer the vehicle. The control motor 26 actuatesthe steering valve 22 correspondingly, and the steering valve, asdisclosed in the aforementioned prior patents, correspondingly actuatesthe steering motor to steer the vehicle in the desired direction.

The control means 50 is shown as including a manually operable steeringwheel 52 which drives a control pump 54 for selectively applying fluidpressure to opposite ends of a fluid operated control valve 56,depending on the direction in which the steering wheel is turned. Thecontrol valve 56 has connected thereto supply and return lines 58 and 60respectively leading from the steering pump 38 and to the reservoir 44.Control lines 62 and 64 extend from the control valve 56 to oppositeends of the control cylinder 28, and deliver fluid under pressure fromthe pump 38 to one side of the control piston 30 or the other, dependingon which way the valve element within the control valve 56 is displacedby clockwise or counterclockwise rotation of the steering wheel 52.

Considering the operation of the power steering system 10 as thus fardescribed, rotation of the steering wheel 52 in one direction or theother results in delivery of fluid under pressure to one end of thecontrol cylinder 28 or the other, thereby either lengthening orshortening the steering valve link 24. Any such variation in the lengthof this link results in corresponding actuation of the steering valve 22to cause it to actuate the steering motor 20 in the correspondingdirection.

It will be understood that, with the foregoing construction, thesteerable means 14 will remain in whatever position it is placed, untilsuch time as the steering wheel 52 is again turned to change theposition of the steerable means. It will also be understood from theaforementioned patents that the steering valve 22 is an open centervalve when the steering wheel 52 is stationary. The same is true of thecontrol valve 56.

Turning now to FIGS. 2 and 3 for a more detailed consideration of thecontrol motor 26, the control cylinder 28 is provided at its ends withaxial cylindrical cavities or recesses 72 and 74 having fluid lines 76and 78 in communication therewith. These fluid lines have check valves80 and 82 therein and communicate with a pressure relief valve or reliefvalve means 84 which, in turn, communicates with the reservoir 44through a line 86.

The control piston 30 is provided on opposite sides thereof with axialcylindrical plungers 92 and 94 respectively complementary to andinsertable into the axial recesses 72 and 74 at the ends of the controlcylinder 28. The plungers 92 and 94 are equipped with Orings, or thelike, to provide fluid-tight seals with the walls of the recesses 72 and74.

Considering the operation of the control motor 26 in conjunction withthe pressure relief valve 84, it will be apparent that, when the controlpiston 30 reaches either end of its stroke, the corresponding plunger 92or 94 enters the corresponding recess 72 or 74 until the fluid trappedin such recess prevents further movement of the control piston. Thus,the fluid trapped in the recess 72 or 74 by the corresponding plunger 92or 94 acts as a hydraulic stop limiting movement of the control piston30. Under normal operating conditions, there is no necessity for anymechanical stop.

However, external forces can occur requiring a greater travel of thecontrol piston 30 than that permitted by the hydraulic stops formed bythe plungers 92 and 94 in the recesses 72 and 74. For example, thesteerable wheel 18 may encounter an obstruction which applies anexternal force tending to cause overtravel of the control piston 30 inone direction or the other. When sufficient pressure is developed in oneof the recesses 72 or 74 as the result of such an external force, thepressure relief valve 84 opens to permit corresponding overtravel of thecontrol piston 30 by permitting the discharge of trapped fluid into thereservoir 44. Ultimately, mechanical stops 96 and 98 on the controlpiston 30 respectively engage mechanical stops 100 and 102 at the endsof the control cylinder 28 to limit the extent of control pistonovertravel in the two directions.

Thus, the invention provides normally operative hydraulic stops whichcan be overridden to permit control piston overtravel when necessary inresponse to external forces. The mechanical stops limit such overtravel.It is important to know that the hydraulic stops have a cushioningeffect on the mechanical stops, limiting the engagement forces involvedat the extreme ends of the control piston stroke.

Although an exemplary embodiment of the invention has been disclosed forpurposes of illustration, it will be understood that various changes,modifications and substitutions may be incorporated in such embodimentwithout departing from the spirit of the invention as set forth in theclaims constituting the next section of this specification.

We claim as our invention:

1. In a fluid operated power steering system for a vehicle having aframe and steerable means subject to external forces, the combinationof:

a. a fluid operated steering motor connected to the steerable means andto the frame;

b. a steering valve link connected to the steerable means and to theframe;

c. said steering valve link including a steering valve connected to andcontrolling said steering motor, and including a control motorcomprising a control cylinder and a control piston;

. manually operable control means for delivering fluid under pressurefrom said pump to said control cylinder on opposite sides of saidcontrol piston selectively;

f. said control cylinder having axial cylindrical recesses at its ends,and said control piston having on opposite sides thereof complementaryaxial h. means connecting said recesses to said reservoir;

and v i. relief valve means in said connecting means for dischargingfluid from said recesses into said reservoir to permit overtravel ofsaid control piston in response to excessive external forces on thesteerable means.

1. In a fluid operated power steering system for a vehicle having aframe and steerable means subject to external forces, the combinationof: a. a fluid operated steering motor connected to the steerable meansand to the frame; b. a steering valve link connected to the steerablemeans and to the frame; c. said steering valve link including a steeringvalve connected to and controlling said steering motor, and including acontrol motor comprising a control cylinder and a control piston; d. apump; e. manually operable control means for delivering fluid underpressure from said pump to said control cylinder on opposite sides ofsaid control piston selectively; f. said control cylinder having axialcylindrical recesses at its ends, and said control piston having onopposite sides thereof complementary axial cylindrical plungersrespectively insertable into said recesses so that fluid trapped in saidrecesses hydraulically stops said control piston at the ends of itsstroke; g. a reservoir connected to said pump; h. means connecting saidrecesses to said reservoir; and i. relief valve means in said connectingmeans for discharging fluid from said recesses into said reservoir topermit overtravel of said control piston in response to excessiveexternal forces on the steerable means.